Parabolic Antenna Feed IlluminationJuly 21st Fact-of-the-Day
An optimal parabolic transmitting antenna converts cylindrical waves radiating from an electromagnetic source (a feed radiator) at is focus into plane waves at its aperture, because plane waves are required if the all radiated energy is to radiate in a single direction toward infinity. If instead the wave front at the aperture is convex, the radiated energy will spread over a range of angles in both planes, or if it is concave, the radiated energy will focus to a near point, crossover, and spread over a range of diverging angles in both planes. Energy reflecting from a perfect parabolic shape will be a plane-wave only if waves illuminating it from a centerline point any distance other than infinity have a cylindrical wave-front. An ideal centerline parabolic feed radiator therefore radiates cylindrical waves. Furthermore, an ideal feed radiator must have a radiation pattern that evenly illuminates a parabola it is used without any of its radiation going in any other direction. ©2005 Martek International All rights reserved.
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